1. Technical Field of the Invention
The present invention relates to an apparatus for manufacturing a band plate that presses edge drop portions at both ends of a plate before rolling, together with a center part of the plate, and leaves edge drops on the plate after rolling.
2. Description of the Related Art
FIGS. 1A and 2 are schematic views of a continuous casting machine of a double-roll type. As shown in these figures, when a slab of a predetermined width is manufactured using a continuous casting machine 50 (strip caster), casting metal in a molten state is passed through two rolls 51 (casting rolls) that rotate in reverse directions. Casting rolls 51 are separated by a predetermined gap that is appropriate for forming the thickness of a slab plate, and are installed in parallel and horizontally.
Molten metal for casting is supplied to a pouring basin formed between side dams 53 disposed between both ends of the casting rolls and a top portion of outer peripheries of casting rolls 51, from an opening of a flat-shaped nozzle 52 of a tundish arranged immediately above (top portion of) the two casting rolls 51. Both side dams 53 are disposed to match the width of the slab to be manufactured, and to prevent molten metal from leaking onto the side surfaces of the ends of casting rolls having the same length as the width of the slab.
The continuous casting machine 50 of a double-roll type manufactures a slab with a predetermined approximate width of 1,200 to 2,000 mm. The continuous casting equipment of a double-roll type can operate using simple ancillary equipment in a compact layout compared to other continuous casting apparatus such as caterpillar-type continuous casting equipment.
When a slab material that has been manufactured with double rolls or a single roll is rolled by a rolling mill 56 downstream on the line, the rolling mill is a conventional non-shifting mill, instead of using a rolling mill in which rolls are shifted in the axial direction of the roll. Conventionally, a roll of the rolling mill has a shape of a parabolic or sinusoidal curve, and have diameters larger at the axial center of the roll than at the ends (barrel-shaped rolls). Barrel-shaped rolls are widely used in a conventional rolling mill to compensate for warping of the pressing roll.
However, the aforementioned continuous casting machine 50 of a double-roll type suffers from a heat crown phenomenon at the casting rolls during casting, because of the long casting roll 51. As a result of this heat crown phenomenon, casting conditions vary along the width of the casting roll. In particular, the variation at the width ends of the work roll becomes greater. Therefore, at the position nearer to the width ends of the roll, the distribution of a plate thickness in the lateral (width) direction of a slab varies more largely.
In addition, because side dams 53 are disposed at both ends of the rolls, heat dissipation efficiencies are high at the roll surfaces that are in contact with side dams; along a lateral section of the slab, portions close to the roll width ends are cooled more efficiently than at the center, so the plate thickness changes from the center to the width ends, resulting in a concave or convex shape. As a result, as shown in FIG. 1B for instance, the section of the slab is tapered at both ends; or conversely, the thickness of the slab may increase at both ends. In the following description, the sectional shape of a slab with tapered ends is called an “edge-drop crown,” and the shape with elevated ends is called an “edge-up crown.”
The inventors of the present invention have already invented a technique and applied it for a patent. This technique is described in Patent literature 1 correcting the edge drop or up crown described above. Patent literature 1 “Band plate manufacturing apparatus” discloses a continuous casting machine of a double-roll or single-roll type, that continuously casts a slab of a predetermined width with molten metal for casting, supplied from a tundish arranged at an upstream location, and a single finish rolling mill that is disposed downstream of the continuous casting machine, and is provided with a pair of up/down work rolls that can move along the axes thereof in opposite directions. As shown in FIG. 3, each of the upper and lower work rolls 61, 62 is shaped for the roll crown such that a diameter of the work roll is made to decrease over a part to one end of the work roll from a position separated by 200 mm from the one end of the work roll, and a diameter of the work roll is made to increase over a part to the other end of the work roll from a position separated by 200 mm from the other end of the work roll. In addition, the work roll profile (outline) between the diameter-changing points is formed as a straight line or an united shape of the straight line and a center convex shape. In other words, each work roll 61 or 62 is a ground crown roll. In addition, both rolls with the roll crown described above are disposed point-symmetrically about a rolling center such that the diameter-decreasing and diameter-increasing part of the upper work roll are respectively positioned at opposite sides of the diameter-decreasing and diameter-increasing part of the lower work roll.
[Patent Literature 1]
Japanese Laid-Open Patent publication No. 11503, 2002
As described above, a plate to be rolled by a rolling mill may have a large edge drop. In particular, a strip caster often produces large edge drops, so slabs manufactured therewith must be specially processed.
Furthermore, edge drops produced by a strip caster can often differ at both ends, because molten metal solidifies differently near both side dams. Therefore, a means for controlling edge drops in a way that differs for left and right side portions is required.
Generally, if the edge drops of a raw material is large and the material is rolled so deeply that edge drops are eliminated, the elongation ratio at a center portion, originally free from edge drops, becomes excessively high, resulting in a problem of undulation produced at the center portion. Therefore, as shown typically in FIG. 4, it is required that both center portion and edge drop portions are rolled so as to leave the edge drops at both end portions after rolling. In FIG. 4, “BEFORE ROLLING” indicates a shape of the plate before rolling, and “AFTER ROLLING” indicates a shape of the plate after rolling.